Due to recent aviation regulations, in particular FAR §25.856 (b), passenger aircraft with a passenger capacity of 20 or greater must be constructed so that they are burnthrough-resistant. This means that for a period of at least four minutes, flame penetration of the aircraft from the exterior to the interior into the cabin must be prevented, for example if after an emergency landing there is a fire on the outside of the aircraft, which fire acts on the aircraft fuselage.
The aluminium aircraft-structures that are commonly used experience burnthrough after approximately 60 seconds so that after this period of time it is possible for flames acting on the aircraft fuselage to enter the interior of the aircraft. In order to prevent this, for the purpose of protecting a passenger cabin, burnthrough-resistant insulation materials for the lower half of the passenger fuselage are mandatory. However, burnthrough-resistant insulation materials that are suitable for this purpose are associated with additional expenditure in the construction of the aircraft, and furthermore result in additional weight because, for example, insulation mats need to comprise special burnthrough-resistant film or foil and film or foil attachment devices. This in turn, overall, increases the aircraft's weight and thus negatively affects the performance, the economy and maintainability of the aircraft. Furthermore, the arrangement of insulation mats that comprise burnthrough-resistant film or foil underneath the cargo compartment region (in the bilge of the fuselage) is not recommended, because a considerable amount of humidity collects in this region, which humidity would be absorbed by the insulation mats. This would result in a gradual increase in the weight of the insulation mats, and drainage would be rendered more difficult.